Although weight gain and obesity are nearly universal features of Cushings syndrome, we hypothesized that screening results would have poor specificity in an obese population. The study is based in a weight loss clinic and enrolled individuals with at least two additional signs or symptoms of Cushings syndrome. 369 subjects (73% female) completed two or three tests: a 24h urine cortisol (UFC), and/or late-night salivary cortisol, and/or 1 mg dexamethasone suppression test (DST). If any result was abnormal (based on laboratory reference range or cortisol after DST >/= 1.8 ug/dl 50 nmol/l), tests were repeated and/or a dexamethasone-CRH (dex-CRH) test was performed. Subjects with abnormal DST results and a low dexamathasone level were asked to repeat the test with 2mg of dexamethasone. We found that in addition to obesity, subjects had a mean of 5-6 features of Cushing's syndrome. None was found to have Cushing's syndrome. Test specificities to exclude Cushing's syndrome for subjects who completed 3 tests were: UFC 96% 95 CI: 93-98%; DST 90% 95 CI: 87-93%; salivary cortisol 84% by RIA 95 CI: 79-89% and 92% by LC-MS/MS 95 CI: 88-95%. The combined specificity (both tests normal) for all combinations of two tests was 84 to 90%, with overlapping confidence intervals. These data do not support widespread screening of overweight and obese subjects for Cushing's syndrome; test results for such patients may be falsely abnormal. Within the same population we are now evaluating the influence of cortisol on parameters of the metabolic syndrome.